Flash discharge apparatus and method

ABSTRACT

This disclosure involves novel flash tubes and similar electric discharge devices and methods comprising electrodes in a gaseous medium between which an electrical discharge is to pass and in which the reliability of repetitive operation is assured through the use of novel cooperative internal initiator conductor means and cooperative external conductive path means at opposite walls of the housing containing the gaseous medium.

United States Patent 1191 Goldberg METHOD lnventor:

Assignee:

Filed:

Appl. No.:

FLASH DISCHARGE APPARATUS AND Jacob Goldberg, Cambridge, Mass.

U.S. Scientific Instruments, Inc. Watertown, Mass,

Dec. 27, 1971 US. Cl 315/204, 313/201, 313/208,

315/330 Int. Cl. H05b 37/00 Field of Search 313/197, 198, 201,

References Cited UNITED STATES PATENTS D. C. POWER SUPPLY IMPEDANCE 12/1959 Edgerton 313/198 X 1111 3,758,819 1 1 Se t. 11, 1973 FOREIGN PATENTS OR APPLICATIONS 865,357 5 1941 France 313/201 x Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl Attorney-Rines and Rines [57] ABSTRACT This disclosure-involves novel flash tubes and similar electric discharge devices and methods comprising electrodes in a gaseous medium between which an electrical discharge is to pass and in which the reliability of repetitive operation is assured through the use of novel cooperative internal initiator conductor means and cooperative external conductive path means at opposite walls of the housing containing the gaseous medium.

11 Claims, 2 Drawing Figures SERIES INJECTION TRIGGER PATENTEDSEPHIQB 3.758.819

QC IMPEDANCE POW FLASH DISCHARGE APPARATUS AND METHOD The present invention relates to flash discharge devices and similar electric-discharge apparatus and methods, being more particularly concerned with gaseous-discharge tubes including flash tubes for stroboscopy, electronic flash photography and similar applications.

The art is replete with many different types of approaches for solving the problem of breaking down or conditioning the gaseous medium of flash tubes and the like in order to discharge therethrough impulses of energy at controlled and precise instants of time,particularly in repetitive applications where such factors as hold-over, gas density and pressure changes, and other erractic behaviour may prevent constant flashes at the desired precise instants of time. An approach to the problem of preventing holdover is described, for example, in U. S. Pat. No. 3,286,128, issued Nov. I5, 1966 to the assignee of the present invention, the tube therein employed involving an array of trigger electrodes for starting the electronic discharge between the principal electrodes of the flash tube. In U. S. Pat. No. 3,355,625, an external breakdown wire is employed with a two-electrode flash tube for improving spurious and non-uniform flashing. Still another approach is represented by U. S. Pat. No. 3,354,351 in which the uniformity of successive flashes is" improved, particularly at high repetition rates, by using the same flashingcontrol device that produces the trigger to apply both the trigger pulse and the stored energy for producing the discharge to the flash tube substantially simultaneously and without dependence upon the breakdown of the flash tube itself.

While these approaches have assisted in improving operation, they still encompass disadvantages that become aggravated when lower-voltage and simpler and smaller equipment is required. Some of these disadvam tages reside in the complexity and number of components involved, in the presence of other electrodes which interfere with the discharge, in the obscuring of portions of the discharge, in the relatively large required magnitude of the trigger flash, and in the suscep tibility to variations in conditions on the surface in the flash tube envelope.

In accordance with the present invention, on the other hand, it has been discovered that, through a novel and rather unexpected cooperative effect between an appropriately connected internal conductive initiator wire or probe, terminating at the inner wall of the flash tube insulating housing, and a cooperative external conductive path along the external wall of the housing, the problem of reliable, highly accurately times, repetitive discharging has been admirably solved. This solution has fastidiously been accompanied by substantially lower requirements in magnitude of trigger flash andother voltages, simpler apparatus requirements and minimum sensitivity to variations in pressure, gas density and other conditions within the flash tube during use.

An object of the present invention, accordingly, is to provide a new and improved flash discharge device and method that shall" not be subject to the abovementioned disadvantages but that, to the contrary, enables a new measure of reliability and relatively low trigger flash operation particularly in repetitive flashing applications.

A further object is to provide a novel electric flash device of more general utility, as well.

Other and further objects will be explained hereinafter and are more particularly delineated in the appended claims. In summary, however, from one of its broad aspects, the invention contemplates a method for producing an electrical discharge between a pair of spaced electrodes within a gaseous medium contained in an insulating-walled housing, that comprises, applying a voltage between the electrodes that, upon triggering of the gaseous medium, may discharge therebetween; disposing a conductive initiator probe connected to one of the electrodes with the free probe end disposed in the gaseous medium next to a point of the inner surface of the insulating wall of the housing; providing a conductive path along the outer surface of the said wall extending from a point thereof opposite the said point of the inner wall surface and connected to the other of the electrodes; and applying a trigger voltage between said initiator probe and said path to develop a highly localized field intensity from the said free probe end to the gas and through the insulating wall between said points to the said opposite point of the conductive path to generate in the gaseous medium enabling the discharge of the applied voltage between the said electrodes. Preferred constructional details are hereinafter set forth.

The invention will now be described with reference to the accompanying drawing, 1

FIG. 1 of which is a combined longitudinal sectio and circuit diagram of a flash tube and its triggering and discharge circuit constructed in accordance with a preferred embodiment of the invention and operating inaccordance with the method thereof; and,

FIG. 2 is a similar diagram of a modification.

Referring to FIG. 1, an anode l and a cathode 3 are shown held spaced from one another within a gaseous medium 5 contained by an insulating tube or housing 7, as of transparent glass or fused quartz or the like in the case of flash tubes. A conventional charging circuit is schematically illustrated comprising energy storage capacitor(s) C and embodying a DC power supply and a series charging impedance, so labelled, for charging the same as described, for example, in the abovementioned patents. Th discharge of the energy stored in the capacitor C between the anode I and cathode 3 is shown effected by a series injection trigger means, so labelled, such as, for example, the boosting circuit described in said US. Pat. No. 3,355,625, or any other well-known trigger circuit.

In accordance with a discovery underlying the present invention, it has been found that a novel type of localized ionization or breakdown effect, different from thecustomary ionization or pre-ionization in the discharge path, and that remarkably conditions the gaseous medium 5 for ready discharge is produced if a pointed or edged initiator wire or probe 2 is appropriately positioned to terminate within the gaseous medium of the tube next to the tube wall. The initiator element 2 is connected at one end to a point P of the anode-supporting structure I rearward of the active anode surface (shown enlarged) opposite the cathode 3, and with the other free pointed or edged end of the initiator element 2'disposed at a point P next to a corresponding point of the insulating inner wall of the housing 7, located such that products of the irradiation and breakdown phenomenon have access to and irradiate the space between the two principal electrodes 1 and 3. In FIG. I, the free point of the initiator element 2 touching the inner wall of the insulating tube envelope or housing at P' is shown disposed opposite the enlarged active anode surface 1 facing the cathode 3, such that ionization-produced irradiation at P can react upon and affect the gaseous medium in the space between the enlarged active anode and cathode surfaces 1 and 3, as later explained.

This breakdown and irradiation phenomenon has been found to occur provided an external conductive path 4 is established, extending from a point opposite the point P along the outer housing wall to the cathode lead support 3 emerging from the flash tube housing 7. The impressed series injection voltage is thus also applied across the part of the insulating tube wall between the initiator element point P and the external conductor surface 4, with great localized field intensity developing at point P because of the concentration provided by that point and the discontinuity in dielectric therefrom to the gaseous medium and to the dielectric of the housing wall itself. This great localized field intensity concentration produces the irradiation that has been found to condition the gas-discharge region between the anode 1 and cathode 3 for ready and remarkably positive breakdown. The connection of the initiator probe 2 at P and that of the conductive path 4 at 3" are external to the discharge region between the electrodes 1 and 3 to prevent spurious ionization effects.

As an example of successful operation of a flash device of such construction, flash tubes of this design have been successfully operated having the following properties and circuit parameters. Trigger voltages of the order of 3-400 volts with DC power supply voltages as low as 200 volts have produced reliable flashing with time jitter only of the order of tens of nanoseconds, the flash tube having a separation between electrodes 1 and 3of 1% millimeters, an outer tube or housing diameter in the larger portions of 25 mm and an overall length of 100 mm, and containing xenon gas at an abso lute pressure of 1% atmospheres. With a similarly di- 1 mensioned conventional tube having the same electrodes and gas pressure, but not having the initiator 2 and cooperative external conductive path 4, trigger voltages are required exceeding kilovolts and with 450 volts or more of DC supply voltage, yielding much larger jitters of the order of hundreds of thousandths of nanoseconds.

The invention, of course, is applicable to tube and electrode geometries of many types, and is not restricted to the particular configuration of FIG. 1. In the embodiment of FIG. 2, as another eaxmple, a long areproducing flash tube is shown, as distinguished from the short, intense discharge arc-producing flash tube of FIG. 1. In FIG. 2, a relatively long and narrow insulating cylindrical flash tube housing is shown at 7', with the anode l and cathode 3 mounted near opposite ends thereof, providing a relatively long discharge path therebetween. The initiator probe 2-is again shown connected muchas in the embodiment of FIG. 1, but this time the external conductive path is in the form of a plurality of circular bands 4 comprising a first band positioned 'in apposition to the point P, and the remaining bands spaced about and at intervals along the tube 7' between the anode l and cathode 3, with a common bus connection 4 connecting the same to the tube cathode 3.

A highly successful tube of the type shown in FIG. 2 employed an envelope 7' of 9 mm outside diameter, an arc length between electrodes 1 and 3 of 9 inches, and filled with xenon gas to an absolute pressure of onefourth of 1 atmosphere. It operated with a DC supply voltage of 1,000 volts,- a series-injection trigger pulse of 2 A kilovolts, and produced a small jitter of less than a 10th of a microsecond. This is to be contrasted with the requirements of prior art trigger circuits with similarly dimensioned flash tubes and gas pressures, but absent the initiator and external conductive path of the present invention, wherein the trigger voltage must be of theorder of 18 kilovolts for the same size DC supply voltage, and wherein the jitter exceeds several microseconds.

Where appropriate, a plurality of initiator probes may also be used, such as, for example, a symmetrically disposed upwardly extending initiator (not shown) in the embodiment of FIG. 1. In some instances, an initiator may also be supplied on the cathode lead, though, in such event, the outer conductive path cooperative therewith will be connected to anode potential.

Further modifications will also occur to those skilled in this art, and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A'method for producing an electrical discharge between a pair of spaced electrodes within a gaseous medium contained in an insulating-walled housing, that comprises, applying a voltage between the electrodes that, upon triggering of the gaseous medium, may discharge therebetween; disposing a conductive intitator probe connected to one of the electrodes with a free probe end remote from said one electrode and disposed in the gaseous medium next to a point of the inner surface of the insulating wall of the housing; providing a conductive path along the outer surface of the said wall extending from a point thereof opposite the said point of the inner wall surface and connected to the other of the electrodes; and applying a trigger voltage between said initiator probe and said path to develop a highly localized field intensity from the said free probe end to the gas and through the insulating wall between said points to the said opposite point of the conductive path to generate in the gaseous medium at said inner wall surface point a localized irradiation that initiates the breakdown of said gaseous medium enabling the discharge of the applied voltage between the said electrodes.

2. A method as claimed in claim 1 and in which the connections of the initiator probe and the conductive path to the respective electrodes is effected at regions external to the discharge space within the gaseous me dium between the said electrodes.

3. A method as claimed in claim 2 and in which the said points are disposed to enable irradiation of the said discharge space by the said generated localized irradiation.

4. A method as claimed in claim 3 and in which the said conductive path is extended from said pointsalong the said outer wall surface toward the said other electrode.

5. A gaseous-discharge device having, in combination, a gas-filled insulating-walled housing containing a pair of spaced electrodes; means for applying a voltage between the electrodes that, upon triggering of the gas,

may discharge therebetween; conducting initiator probe means connected at one end to one of the electrodes and disposed with a free end remote from said one electrode in the gas next to a point of the inner wall surface; conductive path means connected to the other of the electrodes and extending along the outer wall surface to a point thereof opposite the first-named point; and means for applying a trigger voltage between said initiator probe means and said conductive path means to develop a highly localized field intensity between said-points in order to generate within the gas at said first-named point a localized irradiation that initiates the breakdown of the gas, enabling the discharge of the applied voltage between the said electrodes.

6. A gaseous-discharge device as claimed in claim 5 and in which the connections of the initiator probe means and the conductive path means to their respective electrodes is effected at regions external to the discharge space between the electrodes.

7. A gaseous-discharge device as claimed in claim 5 and in which the said points are disposed such as to enable the localized irradiation to irradiate into the discharge space between the electrodes. v

8. A gaseous-discharge device as claimed in claim 7 and in which the said conductive path means extends from said point of the outer wall surface therealong to the region of the housing at which connection is made to the said other electrode.

9. A gaseous-discharge device as claimed in claim 8 and in which the connection at said region is made external to the housing.

10. A gaseous-discharge device as claimed in claim 7 and in which the said initiator probe means is connected to the said one electrode within the said housing.

11. A gaseous-discharge device as claimed in claim 7 and in which said conductive path means comprises a plurality of bands spaced about and along said housing and connected together.

* 1k It t 

1. A method for producing an electrical discharge between a pair of spaced electrodes within a gaseous medium contained in an insulating-walled housing, that comprises, applying a voltage between the electrodes that, upon triggering of the gaseous medium, may discharge therebetween; disposing a conductive intitator probe connected to one of the electrodes with a free probe end remote from said one electrode and disposed in the gaseous medium next to a point of the inner surface of the insulating wall of the housing; providing a conductive path along the outer surface of the said wall extending from a point thereof opposite the said point of the inner wall surface and connected to the other of the electrodes; and applying a trigger voltage between said initiator probe and said path to develop a highly localized field intensity from the said free probe end to the gas and through the insulating wall between said points to the said opposite point of the conductive path to generate in the gaseous medium at said inner wall surface point a localized irradiation that initiates the breakdown of said gaseous medium enabling the discharge of the applied voltage between the said electrodes.
 2. A method as claimed in claim 1 and in which the connections of the initiator probe and the conductive path to the respective electrodes is effected at regions external to the discharge space within the gaseous medium between the said electrodes.
 3. A method as claimed in claim 2 and in which the said points are disposed to enable irradiation of the said discharge space by the said generated localized irradiation.
 4. A method as claimed in claim 3 and in which the said conductive path is extended from said points along the said outer wall surface toward the said other electrode.
 5. A gaseous-discharge device having, in combination, a gas-filled insulating-walled housing containing a pair of spaced electrodes; means for applying a voltage between the electrodes that, upon triggering of the gas, may discharge therebetween; conducting initiator probe means connected at one end to one of the electrodes and disposed with a free end remote from said one electrode in the gas next to a point of the inner wall surface; conductive path means connected to the other of the electrodes and extending along the outer wall surface to a point thereof opposite the first-named point; and means for applying a trigger voltage between said initiator probe means and said conductive path means to develop a highly localized field intensity between said points in order to generate within the gas at said first-named point a localized irradiation that initiates the breakdown of the gas, enabling the discharge of the applied voltage between the said electrodes.
 6. A gaseous-discharge device as claimed in claim 5 and in which the connections of the initiator probe means and the conductive path means to their respective electrodes is effected at regions external to the discharge space between the electrodes.
 7. A gaseous-discharge device as claimed in claim 5 and in which the said points are disposed such as to enable the localized irradiation to irradiate into the discharge space between the electrodes.
 8. A gaseous-dischaRge device as claimed in claim 7 and in which the said conductive path means extends from said point of the outer wall surface therealong to the region of the housing at which connection is made to the said other electrode.
 9. A gaseous-discharge device as claimed in claim 8 and in which the connection at said region is made external to the housing.
 10. A gaseous-discharge device as claimed in claim 7 and in which the said initiator probe means is connected to the said one electrode within the said housing.
 11. A gaseous-discharge device as claimed in claim 7 and in which said conductive path means comprises a plurality of bands spaced about and along said housing and connected together. 